The invention relates to an electro-optical device comprising at least a cell with an electro-optical medium between two supporting plates provided with drive electrodes or picture electrodes, a drive electrode or picture electrode on one of the supporting plates being divided into k sub-electrodes having a surface ratio of 1:2: . . . 2.sup.k-1, k.gtoreq.2.
The invention also relates to a display device comprising such an electro-optical device.
Display devices of the type described can be used for displaying alphanumerical information or video images. The device in itself can be used as an optical shutter in, for example, printers.
A device of the above-mentioned type is described in EP-A-0,316,774. The device described in this application is driven by means of the so-called multiplex drive mode in which in a system of selection lines or address lines (row electrodes) and data lines (column electrodes) perpendicularly crossing one another the drive is effected by alternately energizing the address lines while the information to be written is presented to the data lines. By dividing the column electrodes into sub-electrodes (for example, in accordance with surface ratios of 4:2:1) different transmission levels (grey scales) can be introduced in such a device.
To be able to introduce a large number of grey scales (for example, more than 50) the number of sub-electrodes per column increases considerably (5 or more). Although this can be obviated to some extent by subdividing the row electrodes into sub-electrodes as well, as is suggested in EP-A-0,316,774, this leads to other problems such as, for example, a smaller number of grey scales to be realised, because one grey scale can be defined in a plurality of ways.